Help! Came Center is messing up my view!

My game is running in landscape mode; my main view controller for shouldAutorotateToInterfaceOrientation, returns YES for UIInterfaceOrientationLandscapeRight and UIInterfaceOrientationLandscapeLeft, NO for anything else.

Everything seems to work fine, until...

I show game a center leaderboard. The leaderboard comes on okay (in landscape mode), but after it gets dismissed, the orientation of my game somehow gets switched to portrait. I can tilt the device and the view rotates back in to landscape, and then will not go in to portrait again (unless I display the learderboard again).